Field
The present disclosure relates generally to solid state light emitters, and more particularly, to dimming control of the solid state light emitter.
Background
Solid state light emitters, such as light emitting diodes (LEDs), are becoming the favored choice for general lighting applications over incandescent lamps and fluorescent fixtures for their lower power demand. An LED converts electrical energy to light. Light is emitted from active layers of semiconductor material sandwiched between oppositely doped layers when a voltage is applied across the doped layers. In order to use an LED chip, the chip is typically enclosed along with other LED chips in a package. In one example, the packaged device is referred to as an LED array. The LED array includes an array of LED chips mounted onto a heat conducting substrate. A layer of silicone in which phosphor particles is embedded is typically disposed over the LED chips. Electrical contact pads are provided for supplying current into the LED array and through the LED chips so that the LED chips can be made to emit light. Light emitted from the LED chips is absorbed by the phosphor particles, and is re-emitted by the phosphor particles so that the re-emitted light has a wider band of wavelengths.
Compact lighting fixtures or modules with solid state light emitters do not contain AC/DC conversion, DC driver, and dimming control circuits due to the heat generated by the light emitter, which can compromise the performance of heat sensitive electronics. Instead, the power and control components are typically arranged externally to the lighting fixture. Installation of solid state light emitters using several external power and control components can complicate the physical installation surrounding the lighting fixture and require added labor. Allowing several light emitters to share power and control components may reduce the number of components to install, but at the cost of surrendering individual power and control to each emitter. In particular, for large lighting installations where remote power control of many lighting fixtures is sought from a central location, maintaining individualized control capability is desirable for flexibility of the lighting system operation.
Designing a solid state lighting module with an AC voltage input can eliminate some of the external components, such as the DC driver. A solid state attenuator or rectifier may be used as a driver for the lighting element. For dimming control, passive control circuit devices (e.g., resistive/capacitive (RC) devices) can be used for dimming the lighting element by detection of the zero crossing points of the VAC input which can then be applied in phase-cut techniques. However, such control circuits are typically installed externally to the lighting fixture, and thus have the same drawback as with DC driven light emitters. In addition, due to minimum current flow requirements of the solid state attenuator, complete dimming may not be achievable. Typical circuits of this type are limited to dimming only down to about 5-10% of the light output before the light emitter simply cuts out because of the minimum current parameters of the attenuator. A dimming control circuit for solid state light emitters that can be contained within the lighting fixture with remote control network capability and that can allow deep dimming between 0 and 10% luminance is needed.